The present invention relates to a reinforced flexible container for transportation and storage of bulk material. The container comprises a conventional flexible container which can be made from woven textile fibers, laminated plastics or textile coated with plastic or the like. It comprises a bottom section, a central section and an upper section with lifting loops, and it can also be equipped with an inner sack of impervious material. The lifting loops can be integral parts of the container itself, but may also comprise separate loops or lifting straps secured to the container.
Several types of such containers for transportation of bulk material are used today. Some of these known containers are used only once, while others can be used several times. Among such known flexible containers are those described in British Pat. No. 1,431,582, published Apr. 7, 1976; and in British Pat. No. 1,475,019, published June 1, 1977, U.S. Pat. No. 4,136,713.
The container according to the above U.S. patent is preferably equipped with an inner sack of impervious material, and preferably the upper section of the container comprises integrated lifting loops and a central filling opening. The special feature of this container is that its bottom section consists of at least two pairs of equally wide flaps which are direct extensions of the container walls, and that such flaps are joined at their lower edges such that the joints thereby formed cross each other at one point. This bottom construction has by dynamic testing been found to endure greater strains than the bottom construction according to the above mentioned British Pat. No. 1,475,019.
For certain applications however, conventional flexible containers do not meet the requirements regarding container strength. For transportation of dangerous material like ammonium nitrate for instance, it is required that the container shall endure a specified drop against a plain floor, etc. without rupturing. By example, Verkehr der Bundesrepublik Deutschland, i.e. the authorities of the German Federal Republic, require that flexible containers having a volume of 250-1250 liters shall endure a drop of 1.2 meter when they are filled with pulverent, dangerous materials. References made to "Amtsblatt der Bundesministers f ,uml/u/ r Verkehr der Bundesrepublik Deutschland", No. 6, page 254-259, of Mar. 31, 1976 volume 30, published in Bonn, Germany. In this application dangerous material means that classified as such in packaging group 3 by the Intergovernmental Maritime Consultative Organization (IMCO).
The disadvantage of the known flexible containers is that they burst just above the bottom when dropped, in filled condition, against a floor etc. Tests have shown that most of them burst already when the drop height is only 0.3 meter.